There are two approaches you can take to this very common problem.
Either one will work. One is more work than the other. And some people say that one is more gentle and humane than the other.
You will need to choose a technique and apply it consistently.
(1) Use your knee
This is the one that even those without dogs know.
The dog approaches you trembling with excitement. He stands up to place his paws on your stomach or chest. You roll to the side just before he can get his paws on you and lift your knee so he meets a hard, pointed but blunt object. After holding onto that for a second or two, he falls to the ground. You win.
There are a couple of additional things you can do at this point.
You can teach him that he gets a nice reception when all four paws are on the ground by squatting next to him when he’s released your knee and giving him plenty of attention and fuss.
And if he gets his paws on you before you can lift your knee, then do your best to appear disinterested. Do not reward your dog in any way. (and that means don’t push him with your hands, as this is a fun game for any dog. Don’t talk to him. Ignore him. Make whatever he wants a game, definitely a non-event.
IT’S OKAY. that’s the knee to his chest. But there is an alternative.
(2) Use your hands
When the dog jumps, this second technique has you grab his legs with both hands and stay there. His jump has suddenly “frozen”. Nothing is happening. There was no reaction. Instead, he has been caught and can’t do anything!
Keep it that way. Hold on to him and don’t move. Draw this. Make it go on as long as you can. Talk to him if you want, but stop him.
Most dogs, after a while, will begin to drool on your hands. This is your signal, drop it. Hard. Do not lower him to the ground, but let him go abruptly.
Then, when he’s on the ground, squat down with him and give him the nice, uplifting moment he was hoping for by jumping up a few moments earlier.
This way he will learn that your best reaction is always when he is on his four legs!